The invention relates to an electric toothbrush with a manually guidable handle part having a motor and a gear, and a push-on brush which is to be fastened thereon and which has a plurality of rotatably arranged bristle holders which each have an eccentric peg engaging in transversely extending grooves in a connecting rod which may be caused to reciprocate in the direction of its longitudinal axis by the gear by means of a toothbrush arbor and a first cam.
U.S. Pat. No. 4,989,287, issued to Scherer on Mar. 5, 1991 and incorporated herein by reference, relates to a toothbrush of this type. With the '287 toothbrush, the push-on brush may be rotatably connected (with respect to its longitudinal axis), by means of a locking connection, onto the front region of the casing of the handle part. The toothbrush arbor and therefore also the connecting rod are caused to oscillate about their longitudinal axis and also to reciprocate in the direction of the longitudinal axis by means of a rocker and a cam engaging therein. The reciprocating movement of the connecting rod is converted into an alternating rotational movement of the tufts of bristles in the brush head of the push-on brush while the oscillating movement of the connecting rod leads to a corresponding oscillating movement of the entire push-on brush.
The drive of the tufts of bristles by a connecting rod leads to problems if the individual tufts of bristles are to be rotated to and fro with a greater angle of rotation. For this purpose, it is necessary to increase the stroke of the connecting rod by increasing the stroke of the toothbrush arbor, and this can give rise to greater eccentricity of the cam of the gear and can therefore lead to an undesirable increase in the size of the gear.
It is known from published PCT International Application No. PCT/EP92/02624 to dispense with the connecting rod for increasing the rotational angle of the tuft of bristles and instead to drive the tufts of bristles by means of a rotatable shaft. However, as toothbrushes with a connecting rod having transverse grooves and eccentric members of the bristle holders engaging therein have proven appropriate, attempts have been mad[e to maintain this principle of production of the alternating rotational movement of the tufts of bristles.